|Publication number||US7196459 B2|
|Application number||US 10/728,671|
|Publication date||Mar 27, 2007|
|Filing date||Dec 5, 2003|
|Priority date||Dec 5, 2003|
|Also published as||CN1624942A, CN100521262C, EP1598591A2, EP1598591A3, US20050122018|
|Publication number||10728671, 728671, US 7196459 B2, US 7196459B2, US-B2-7196459, US7196459 B2, US7196459B2|
|Inventors||Thomas M. Morris|
|Original Assignee||International Resistive Co. Of Texas, L.P.|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (22), Referenced by (40), Classifications (39), Legal Events (7)|
|External Links: USPTO, USPTO Assignment, Espacenet|
This invention relates to an improved light emitting assembly having a heat dissipating support for reducing the operating temperature of the assembly.
Light sources are evolving toward assemblies of light emitting elements such as light emitting diodes which are known in the art as LED's. Assemblies of LED's are being used or will be used in many high volume applications because they produce substantial light in proportion to the power consumed, are long lived and are extremely reliable. One such application is light sources for vehicles, such as headlights, taillights and directional signal lights. Other applications include replacements for florescent and incandescent lights and the like.
High output LED's, particularly when a large number are used on a common support, have a problem because they produce a significant amount of heat and the current generation of LED's begin to lose brightness when they are hotter than about 100° C. There are two current approaches to dissipate heat in commercially produced high output LED assemblies. The first is to apply the LED's to a circuit board which is glued to an aluminum heat sink. This is not a particular efficient technique for dissipating heat because the circuit board and the glue are tolerably good thermal insulators thereby insulating the heat source from the heat sink. The second is to apply the LED's to an epoxy layer bonded to an aluminum plate. The epoxy layer acts as an electrical insulator for electrical reasons but it is likewise a good thermal insulator thereby insulating the heat source from the heat sink.
It has been proposed in U.S. Pat. No. 5,857,767 to apply LED's to an aluminum heat sink which is anodized or which is coated with an electrically insulating layer by using a thermally conductive adhesive, i.e. an adhesive having dispersed metallic particles. There are several problems with this approach. First, conductive adhesives are inferior to solder in both electrical and thermal conductivity. Second, the electronics assembly process requires two steps, one to attach those components that are preferably soldered and one to attach those components which must be adhesively secured.
Disclosures of interest are found in U.S. Pat. Nos. 4,628,422; 4,729,076; 4,742,432; 4,935,665; 5,528,474; 5,632,551; 5,782,555; 5,785,418; 6,016,038; 6,045,240; 6,161,910; 6,435,459; 6,480,389; 6,517,218 and 6,582,100.
In this invention, a light emitting assembly includes a substrate or heat sink, a series of circuit traces on the substrate and one or more light emitting elements. The substrate or heat sink is a metal which is coated with a thin electrically insulating layer. Preferably, the metal is anodized to produce the electrically insulating layer. The metal may be of any suitable type but preferably is an anodizable type such as aluminum, magnesium and their alloys. The substrate is anodized in a conventional manner to produce a thin, tough electrically insulating coating bonded directly to the underlying metal. Anodized aluminum substrates have three powerful advantages: low cost, structural strength and high heat dissipating capacity. In some situations, the substrate is masked to provide sections with no anodized layer to provide a direct thermal path from the LED to the substrate. In addition, masked sections of the substrate may be used to reflect light from the LED's thereby increasing the amount of light emitting from the assembly and reducing the amount of energy absorbed by the substrate.
The circuit traces of the LED assemblies of this invention may be made either by thin or thick film techniques, depending on the application. Thin film techniques are more expensive but are capable of producing devices capable of operating at higher voltages because the electrically insulating layer is not degraded by the heat processes needed in the manufacture of thick film devices. In addition, thin film techniques allow for smaller line widths, known as finer geometries, which result in more components per unit area. As is known in the art, conventional thin film techniques apply circuit traces to the electrically insulated substrate by vapor deposition or sputtering of conductive materials onto the substrate.
Thick film techniques tend to produce low cost assemblies which have a feature size down to about 100 microns. As is known in the art, conventional thick film techniques apply circuit traces by applying inks to the electrically insulated substrate, typically by screen printing or direct writing techniques, and then curing the inks in an oven. Thus, circuit traces are applied by either thick or thin film techniques to the substrate to provide current paths between the LED's, the power supply and any other circuitry or components that may be necessary or desirable in the operation of the end product.
As will become apparent, an important feature of this invention is the use of silver or a silver based material to provide the circuit traces and to provide a shiny metallic patch beneath or adjacent the LED's. Silver based circuit traces can be soldered or wire-bonded with conventional techniques so all connections can be made in one process step. Because the silver patches are prone to tarnish in air, the silver patches are overprinted with a clear lacquer. Thus, the silver patches increase reflectivity of the substrate, minimize energy absorption by the substrate and maximize light emitting from the assembly. As used herein, the phrase silver rich coating is intended to mean coatings of silver or silver based materials such as a mixture of silver and glass.
Some commercially available LED's are available that include an internal reflector and a metallic heat transfer element on the bottom of the device. Other commercially available LED's do not include the internal reflector and/or the heat transfer element. In both situations, assemblies of this invention incorporate a metallic section adjacent the base of the LED to abut the metallic heat transfer element and thereby improve heat dissipation or to reflect light from the LED that would otherwise be absorbed by the substrate and thereby increase the amount of light emitting from the assembly. In the alternative, areas of the electrically insulating layer or anodized layer may be masked during their application to expose the bare metal substrate to the LED thereby to improve heat dissipation and/or to improve reflectivity.
The leads from the LED's are connected to the circuit traces by conventional soldering or wire-bonding. This is accomplished by making the circuit traces of a material compatible with soldering or wire-bonding and/or to apply a metallic section to the terminals of the circuit traces which are compatible with soldering or wire-bonding. Soldering and wire-bonding are preferred techniques for securing the LED's to the substrate because they are easily automated, can be done at the same time other components ar soldered or wire-bonded to the substrate and they provides a durable connection of high thermal and electrical conductivity. The result of this invention is an improved LED assembly incorporating an efficient heat dissipating substrate.
It is an object of this invention to provide an improved light emitting assembly.
Another object of this invention is to provide an improved light emitting assembly incorporating a metal substrate having an electrically insulating coating, one or more circuit paths applied to the coating and one or more light emitting elements soldered or wire-bonded to the circuit paths.
A further object of this invention is to provide an improved light emitting assembly in which a current limiting resistor is incorporated into assembly.
Another object of this invention is to provide an improved light emitting assembly in which a plurality of silver patches are applied to an electrically insulated metal substrate and act as reflectors of light emitting from the light emitting elements.
These and other objects of this invention will become more fully apparent as this description proceeds, reference being made to the accompanying drawings and appended claims.
The substrate or heat sink 12 may be of any suitable metal that has appropriate heat dissipating characteristics, strength, cost and the ability to receive a thin electrically insulating layer or coating 18. Preferred metals include aluminum, aluminum alloys, magnesium, magnesium alloys, zinc, pot metal and the like. The electrically insulating coating 18 is formed with a thickness of ten microns to one thousand microns, preferably on the order of about fifty to one hundred microns. The electrically insulating coating 18 may be of any suitable type and may be applied in any suitable manner. The coating 18 may be applied by screen printing and then fired in an oven, may be applied in a plasma spraying technique or may be applied as a porcelain enamel. Preferably, however, the coating 18 is an anodized coating, meaning that the metal of the substrate 12 is preferably an anodizable metal such as aluminum, magnesium and their alloys. The optimum material for the substrate is an anodized aluminum alloy because of its combination of high heat dissipating capacity, structural strength and low cost. The substrate 12 includes a flat surface which is necessary or convenient to apply thin or thick film layers and may include heat dissipating fins, corrugations, or other irregular area increasing undulations on a side opposite the flat side to increase the heat rejecting capacity of the substrate 12.
The circuit traces 14 may be either thick or thin film coatings applied by conventional techniques. Low voltage devices are typically made using thick film techniques where an ink is applied by printing techniques to the coating 18. Conventional printing techniques include screen printing, direct writing and the like. After printing, the substrates are passed through an oven to fire the ink, causing the glass component of the thick film ink to melt, to produce adherent electrically conductive circuit traces or paths 14 on the coating 18. Firing the substrate 12 at temperatures above about 400° C. in the process of curing the ink degrades the electrical insulating properties of the anodized layer 18. For this reason, higher voltage devices are made by thin film techniques in which adherent electrically conductive circuit traces are deposited by sputtering, vapor deposition or other suitable thin film techniques that do not require high temperatures. The phrase thin film is known in the art to refer to processes and products where the layers are on the order of 200 to 20,000 Angstroms. The phrase thick film refers to processes and products where the layers are on the order of eight to fifty microns.
The circuit traces 14 extend between various terminals 22, 24, 26 at the ends of the traces 14 to provide the desired circuitry of the assembly 10. In thin film devices, the circuit traces 14 and terminals 22, 24, 26 are preferably silver to provide high conductivity, compatibility with soldering or wire-bonding operations and high reflectivity. In thick film devices, the circuit traces 14, terminals 22, 24, 26 are made by printing a silver based ink onto the anodized layer 18 and then firing the ink. A suitable silver based ink is a silver-glass-carrier mixture available from Metech Polymers of Elverson, Pa. and is known as Type 3270. The circuit traces 14 and the terminals 22, 24, 26 are accordingly preferably of the same material and laid down at the same time during the same process step.
Some of the terminals 26 may be located on the edge of the substrate 12 and may be secured, as by soldering or the like, to connectors (not shown) extending off the side of the assembly 10, at least one of which extends to a power source. In the alternative, the terminals 26 may be connected through circuit traces (not shown) below the traces 14. In the event circuit traces (not shown) are provided below the traces 14, an electrically insulating layer is applied and then cured to provide an electrically insulated base for the traces 14. One or more additional components may be located in an area 28 on the substrate 12 in the event additional functions are required by the assembly 10.
An important feature of this invention is the ability to incorporate a current limiting resistor 29 in the circuit of the assembly 10. The resistor 29 is of the thick or thin film type depending on the selection for the circuit traces 14 and comprises a suitable resistive material such as tantalum nitride. Because the substrate 12 is particularly suited to accommodate high temperatures, the inclusion of the resistor 29, in a small size, presents no thermal problems.
A metallic patch or section 30 is provided beneath or adjacent the LED 16 to transmit heat away from the LED 16 and/or to reflect light from the LED away from the substrate 12. An important feature of this invention is that the circuit traces 14, the terminals 24, 26, 28 and the patches 30 are silver in the case of thin film devices and a silver based material in thick film devices. Making these elements of silver provides compatibility with metal droplet connections, such as soldering or wire bonding, provides good thermal conductivity between the LED and the metal substrate 12 and reflects a significant amount of light emitting from the LEDs thereby maximizing the amount of useable light and minimizing the amount of energy transferred to the substrate.
The patch 30 is preferably made of the same material as the circuit traces 14 and terminals 22, 24, 26 so it may be laid down at the same time and during the same process step as the traces 14 and the terminals 22, 24, 26. To minimize tarnishing of the patches 30, they are preferably coated with a clear or transparent finish, such as lacquer 31. As shown best in
As shown best in
In the embodiment of
It will be evident that if the LED 16 were of the type that did not have an internal reflector 34, the metal patch 30 acts as a reflector of light emitting from the LED because is shiny and silver.
It will be evident that if the LED 42″ were of the type that did not have an internal reflector 44″, the substrate 12″ exposed through the opening 48 provides a suitable reflector, particularly when the substrate 12″ is a light colored shiny metal, such as aluminum, magnesium and their alloys. In this event, the substrate 12″ may be coated with a clear or transparent finish, such as lacquer 31″, to prevent the substrate 12″ from tarnishing in an area where reflectivity is important.
The LED 62 abuts or is otherwise in thermal contact with the electrically insulating coating 54 as allowed by the opening 60 in the circuit trace 56 and is thus in thermal contact with the metal substrate 52. The slits 68 between adjacent circuit traces 56 are sufficient to electrically separate the traces 56 so any electrical current passes through the LED 62. To minimize tarnishing of the circuit traces 56, a clear finish 70 is applied, either by masking off a section where soldering is to be done or, after soldering has been done, over substantially the entire circuit traces 56.
The test panel 50 also includes two four LED assemblies 72, 74 although those skilled in the art will recognize that as many LED's can be incorporated into an array as is desired. The pattern of the slits 76, 78 in the circuit traces 80, 82 is selected, based on the LED's 84, 86 being placed in series. Thus, the slits 76, 78 divide the circuit traces 80, 82 into segments which are electrically connected by the LED's 84, 86 and their leads 88, 90 which are soldered or wire-bonded to the circuit traces 80, 82. The circuit traces 80, 82 provide terminals 92, 94 which connect by conventional arrangements with a power providing circuit. To minimize tarnishing of the circuit traces 80, 82, a clear finish 96, 98 is applied, either by masking off a section where soldering is to be done or, after soldering has been done, over substantially the entire circuit traces 80, 82.
It will be seen that the gap separating the circuit traces may be varied substantially for a variety of reasons, such as to provide a three terminal device 122. The gap 123 divides the silver layer into sections 124, 126, 128 allowing three leads to be soldered or wire-bonded to the device 122. To minimize tarnishing of the circuit traces 124, 126, 128, a clear finish 130 is applied, either by masking off a section where soldering is to be done or, after soldering has been done, over substantially the entire circuit traces 124, 126, 128.
Other LED configurations or circuit trace configurations may be provided, as shown by the substrate 132 in
It will be seen that this invention provides a light emitting assembly having an efficient technique for dissipating heat and for reflecting light from the light emitting elements.
Although this invention has been disclosed and described in its preferred forms with a certain degree of particularity, it is understood that the present disclosure of the preferred forms is only by way of example and that numerous changes in the details of construction and operation and in the combination and arrangement of parts may be resorted to without departing from the spirit and scope of the invention as hereinafter claimed.
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|U.S. Classification||313/46, 362/294|
|International Classification||F21K99/00, H05K3/28, F21S8/10, H05K1/02, F21Y101/02, H01L33/00, H05K1/09, F21S8/00, F21V29/00, H05K1/05, H05K1/18|
|Cooperative Classification||F21K9/00, F21S48/328, H05K3/28, H05K2201/2054, F21V29/004, F21S48/10, F21V29/763, H05K1/092, H05K1/0204, H05K1/053, H05K2201/10969, F21W2111/00, H05K1/0274, H05K1/182, F21Y2101/02, H05K2201/10106, H05K1/021, F21S48/215, H05K2201/09781|
|European Classification||H05K1/02G, H05K1/02B2G, F21S48/32P, F21K9/00, F21V29/22B2F2, H05K1/02B2B, F21V29/00C2|
|Mar 23, 2004||AS||Assignment|
Owner name: INTERNATIONAL RESISTIVE CO. OF TEXAS, LP, TEXAS
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:MORRIS, THOMAS M.;REEL/FRAME:015121/0936
Effective date: 20031128
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